Touch zones screens of the type described above are commonly used, particularly in combination with the display screens of some portable electronic apparatus, such as telephones and watches with a touch glass. By arranging a touch zone screen above the display screen, it is possible to control various electronic functions of the associated portable device.
Capacitive touch zone screens operate in accordance with the principle of capacitance variation, which is observed when the user moves his finger towards the desired electrode. This capacitance is inversely proportional to the distance that separates the electrode concerned from a corresponding counter-electrode, the intersection of said electrode with said corresponding counter-electrode defining the touch zone. It is thus crucial to be able to control this distance with the highest level of precision so that the electronic control circuit of the portable apparatus can interpret the capacitance variation properly as corresponding to the introduction of a command.
Another problem with touch zone screens lies in the fact that although they are made of transparent material, the electrodes are always at least partially visible, notably because of ambient light reflections on the touch screen. These reflections are detrimental to the general appearance of the apparatus and can interfere with the visibility of information displayed on the display screen of the apparatus.
It is an object of the present invention to overcome the aforementioned problems, in addition to others, by providing a capacitive touch-zone screen, wherein an associated electronic circuit interprets the control signals without causing any errors or malfunction. The present invention also provides a capacitive touch screen whose electrodes are invisible or practically invisible to the user.